• Journal of Welding and Joining
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• 제26권1호
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• pp.76-82
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• 2008

The effect of Nb addition on the precipitation and precipitate coarsening behavior was investigated in Ti and Ti + Nb steel weld HAZ. A dilatometer equipped with a He-quenching system was used to simulate the weld thermal cycle. Compared to $TiC_yN_{1-y}$ precipitate in a Ti containing steel, $Ti_xNb_{1-x}C_yN_{1-y}$ complex particle with addition of Nb is precipitated in a Ti + Nb containing steel. Meanwhile, precipitate coarsening occurred more easily in Ti + Nb steel, which may be because the high temperature stability of $Ti_xNb_{1-x}C_yN_{1-y}$ complex particle is deteriorated by the Nb addition.

• 한국재료학회지
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• 제3권1호
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• pp.43-49
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• 1993

AI킬드한 극저탄소강에 Ti, Nb등의탄화물 또는 질화물 형성원소를 첨가하면 우수한 디프드로잉특성과 내시효성을 나타내는 강판을 얻을 수 있다고 알려져 있으므로 본 연구에서는 Ti및 Nb를 단독 또는 동시에 첨가하거나 B를 추가로 첨가한 고강도 극저탄소 강판을 제조하여 각각의재결정 집합조직과 기계적 성질을 측정비교하여 보았다. 역극점도에 나타난 집합조직강도의 변화를 조사한 결과 어닐링처리에 의하여 (100)면 강도와 (111)면 강도의 변화가 가장 많이 나타난 것은 Nb첨가강이며, Nb와 Ti를 단독으로 첨가한 강과 Ti를 단독으로 첨가한 강은 변화정도가 비슷하였다.극점도를 비교하면,Nb와 Ti를 동시에 첨가한강, Nb를 단독으로 첨가한 강 그리고 Ti를 단독으로 첨가한강 모두 냉간 압연한 상태에서는{112}<110>집합조직이 발달하였으며 어닐링처리한 후에는 {111}<112>집합조직이 잘 발달하였다. 그러나 세 종류의 강간에 집합조직의 차이는 별로 없었다. 결정립도와 관계가 깊은 경도에서는 결정립도가 가장 작은 Nb 및 Ti동시첨가강에서 경도가 가장 높고, Nb단독첨가강, Ti단독첨가강의 순서로 감소하는 경향을 보였다.

• 한국재료학회지
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• 제3권2호
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• pp.131-139
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• 1993

극저탄소 알루미늄 킬드강내에 합금원소로 첨가된 Al, Ti, Nb, B등은 열처리 공정중 질화물이나 탄화물로 석출되어 강의 재결정집합조직을 변화시킴으로써 강판재의 디입드로잉 특성에 결정적인 영향을 미친다. 본 연구에서는 Ti및 Nb를 단독으로 또는 동시에 첨가한 데 이어, B, P, Si 및 Mn등을 추가로 첨가한 극저탄소 고강도 강판의 집삽조직에 미치는 질화물, 탄화물과 같은 미세 석출물의 영향을 TEM, SEM, 광학현미경분석에 의하여 조사하였다. Nb 및 Ti를 동시에 첨가한 강에서는 미세한 N$b_2$C 및 T$i_2$AIN가 주로 석출되는 반면, Nb를 단독으로 첨가한 강에서는 미세한 AIN 및 조대한 BN이 석출되고,Ti를 단독으로 첨가한 강에서는 비교적 조대한 T${i_4}{N_3}$및 조대한 ${N_10}{N_22}$/T$i_68$이 석출되는 것으로 관찰되었다. 또한 이러한 탄질화물들의 석출에 의하여 세 강이 서로 다른 결정입도를 나타내는데, 결정입도는 Nb 및 Ti동시첨가강과 Nb단독첨가강이 서로 비슷하고, Ti단독첨가강이 가장 큰 것으로 나타났다.

• 한국표면공학회지
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• 제35권6호
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• pp.391-400
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• 2002

Corrosion characteristics of Ti, Ti/Cr coated and plasma-nitrided surface for stainless steel containing Ti have been studied. Stainless steels containing 0.09-0.92wt% Ti were fabricated by using vacuum furnace and solutionized for 1hr at 105$0^{\circ}C$. Ti and Cr coatings were done on solutionized stainless steel surface by EB-PVD. The Ti coated specimen were coated by Cr and were nitrided by plasma at $450^{\circ}C$ for 5hr. Microstructure and phase analysis were performed using SEM, OM and EDX. Corrosion behavior of the coated specimen was investigated by electrochemical test. The coated surface was of fine columnar structure. The Ti/Cr coated surface was denser than the Ti coated and the Ti coated-nitrided surfaces. The corrosion and pitting potential increased in proportion to the Ti content, coating temperature, coating thickness and formation of stable oxide film. The current density in active and passive region decreased in the case of Ti/Cr coated sample and Ti coated-nitrided samples. Especially the plasma nitrided specimen after Ti coating have a good corrosion resistance compared with the Ti coated specimen. The number and size of pits decreased as Ti content of matrix increased.

• 한국표면공학회지
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• 제36권1호
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• pp.89-98
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• 2003

Corrosion characteristics of Ti, Ti/Cr coated and plasma-nitrided surface for stainless steel containing Ti have been studied. Stainless steels containing 0.09-0.92wt% Ti were fabricated by using vacuum furnace and solutionized for 1hr at $1050^{\circ}C$. Ti and Cr coatings were done on solutionized stainless steel surface by EB-PVD. The Ti coated specimen were coated by Cr and were nitrided by plasma at $450^{\circ}C$ for 5hr Microstructure and phase analysis were performed using SEM, OM and EDX. Corrosion behavior of the coated specimen was investigated by electrochemical test. The coated surface was of fine columnar structure. The Ti/Cr coated surface was denser than the Ti coated and the Ti coated-nitrided surfaces. The corrosion and pitting potential increased in proportion to the Ti content, coating temperature, coating thickness and formation of stable oxide film. The current density in active and passive region decreased in the case of Ti/Cr coated sample and Ti coated-nitrided samples. Especially the plasma nitrided specimen after Ti coating have a good corrosion resistance compared with the Ti coated specimen. The number and size of pits decreased as Ti content of matrix increased.

• 한국표면공학회지
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• 제38권6호
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• pp.227-233
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• 2005

Electrochemical characteristics of welded stainless steels containing Ti have been studied by using the electrochemical techniques in 0.5 M $H_2SO_4$+0.01 M KSCN solutions at $25^{\circ}C$. Stainless steels with 12 mm thick-ness containing $0.2{\~}0.9 wt\%$ Ti were fabricated with vacuum melting and following rolling process. The stainless steels were solutionized for 1hr at $1050^{\circ}C$ and welded by MIG method. Samples were individually prepared with welded zone, heat affected zone, and matrix for intergranular corrosion and pitting test. Optical microscope, XRD and SEM are used for analysing microstructure, surface and corrosion morphology of the stainless steels. The welded zone of the stainless steel with lower Ti content have shown dendrite structure mixed with $\gamma$ and $\delta$ phase. The Cr-carbides were precipitated at twin and grain boundary in heat affected zone of the steel and also the matrix had the typical solutionized structure. The result of electrochemical measurements showed that the corrosion potential of welded stainless steel were Increased with higher Ti content. On the other hand, reactivation($I_r$), passivation and active current($I_a$) density were decreased with higher Ti content. In the case of lower Ti content, the corrosion attack of welded stainless steel was remarkably occurred along intergranular boundary and ${\gamma}/{\delta}$ phase boundary in heat affected zone.

• 한국재료학회지
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• 제19권9호
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• pp.473-480
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• 2009

In order to provide the mechanism of nozzle clogging, recovered nozzles for high strength steel grade were examined carefully after continuous casting. The thickness of clogged material in SEN is increased in the following order: from the bottom to the top of the nozzle, upper part of slag line, and the pouring hole. Nozzle clogging material begins to form due the adhesion of metal to nozzle wall, the decarburization, and reduction of oxide in the refractory by Al and Ti in the melt. The reduction of oxide in the refractory by Al and Ti improves the wettability of the melt on the refractory and forms a thin Al-Ti-O layer. Metal containing micro alumina inclusions is solidified on the Al-Ti-O layer, and the solid layer grows due to the heat evolution through the nozzle wall. Thermodynamic calculation has been made for the related reactions. The effect of superheat to the nozzle clogging is discussed on ultra low carbon steel and low carbon steel.

• 한국표면공학회지
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• 제37권6호
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• pp.350-359
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• 2004

Stress corrosion cracking(SCC) characteristics of shot-peened stainless steel containing Ti (0.09 wt%-0.92 wt%) fabricated by the vacuum furnace were investigated using SCC tester and potentiostat. The homogenization and the sensitization treatment were carried out at $1050^{\circ}C$ for 1hr and $650^{\circ}C$ for 5 hr. The samples for SCC were shot-peened using $\Phi$0.6 mm steel ball for 4 min and 10 min. Intergranular and pitting corrosion characteristics were investigated by using EPR and CPPT. SCC test was carried out at the condition of$ 288^{\circ}C$, 90 kgf pressure, water with 8 ppm dissolved oxygen, and $8.3xl0^{-7}$/s strain rate. After the corrosion and see test, the surface of the tested specimen was observed by the optical microscope, TEM and SEM. Specimen with Ti/C ratio of 6.14 showed high tensile strength at the sensitization treatment. The tensile strength decreased with the increase of the Ti/C ratio. Pitting and intergranular corrosion resistance increased with the increase of Ti/C ratio. Stress corrosion cracking strength of shot-peened specimen was higher than that of non shot- peened specimen. Stress corrosion cracking strength decreased with the increase of the Ti/C ratio.

• Journal of Welding and Joining
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• 제20권3호
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• pp.91-97
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• 2002

Variation of HAZ toughness of Ti-containing steel with nitrogen content was investigated and interpreted in terms of its microstructure and the amount of soluble nitrogen present. The amounts of Ti and Al combined in TiN and AlN, respectively, in HAZ at $1400^{\circ}C$ peak temperature were less than those in base plate; 55~88% in TiN and 21~28% in AlN, indicating the dissolution of nitrifies in HAZ. The calculated amounts of soluble nitrogen using the thermodynamic analysis showed a good agreement with the measured values in other experiment. Therefore, the analysis can be used to estimate the amount of soluble nitrogen in HAZ. Simulated HAZ toughness was influenced not only by its microstructure but also by the amount of soluble nitrogen present after the formation of BN during the cooling cycle of welding. It showed maximum value when the nitrogen content is in stoichiometric ratio with titanium content, showing that soluble nitrogen in HAZ is detrimental to its toughness.

• 한국표면공학회지
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• 제33권2호
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• pp.93-100
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• 2000

Effects of Ti content and Ti underlayer on the pitting behavior of TiN coated AISI 304 stainless steel have been studied. The stainless steel containing 0.1~1.0wt% Ti were melted with a vacuum melting furnace and heat treated at $1050^{\circ}C$ for 1hr for solutionization. The specimen were coated with l$\mu\textrm{m}$ and 2$\mu\textrm{m}$ thickness of Ti and TiN by E-beam PVD method. The microstructure and phase analysis were conducted by using XRD, XPS and SEM with these specimen. XRD patterns shows that in TiN single-layer only the TiN (111) Peak is major and the other peaks are very weak, but in Ti/TiN double-layer TiN (220) and TiN (200) peaks are developed. It is observed that the surface of coating is covered with titanium oxide (TiO$_2$) and titanium oxynitride ($TiO_2$N) as well as TiN. Corrosion potential on the anodic polarization curve measured in HCl solution increase in proportion to the Ti content of substrate and by a presence of the Ti underlayer, whereas corrosion and passivation current densities are not affected by either of them. The number and size of pits decrease with increasing Ti content and a presence of the coated Ti film as underlayer in the TiN coated stainless steel.